Foams and, in particular, foam emulsions are complex dispersion systems which do not form under all circumstances. Slight shifts in foam emulsion composition, such as by the addition of active ingredients, may destabilize the foam.
Micro emulsions and nano emulsion can be monophasic, transparent (or slightly translucent) dispersions of oil and water. Unlike conventional emulsions, micro emulsions and nano emulsion can be thermodynamically stable, making them a favorable vehicle for pharmaceutical compositions, which have to maintain stability for long periods of time. Micro emulsions are sometimes said to be misleadingly called micro emulsions since they can form clear solutions devoid of the opaque color of regular emulsions. Micro emulsions can be oil external, water external and middle phase. Nano emulsions in contrast can be very fine oil in water dispersions. Droplet diameters can be as low as smaller than 100 nm. They can be in a metastable state and their structure can depend on the system history. They can be very fragile systems and can therefore be problematic in trying to formulate pharmaceutical and cosmetic compositions. If destabilized they can become opaque or exhibit creaming. On the other hand they can provide useful applications in skin care in that they may exhibit good textural and sensural properties due to the very fine droplet or globule size. Likewise for similar reasons they may provide more rapid penetration than conventional emulsions and can offer hydrating capabilities.
Foams are very complex and sensitive systems and are not formed at will. Mere addition of basic ingredients like oil, water, surfactant and propellant is far from sufficient to produce foams of quality that are homogenous, stable, breakable upon mechanical force and can be used to provide a shelf stable pharmaceutical or cosmetic composition. Small deviations may lead to foam collapse. Much consideration needs to be given to facilitate the introduction of an active agent, such as examining compatibility and non reactivity with the various excipients and container and determining shelf life chemical stability. All these considerations become a greater and more non obvious challenge when trying to formulate a foamable nano-emulsion composition, which demands the symbiosis and compatibility of a complex, sensitive system with a fragile and metastable system to produce a homogenous, stable, breakable shelf stable nano foam. Moreover, nano droplets can be sterilized by filtration.
Storage triacylglycerols (TAG) in plant seeds are present in small discrete intracellular organelles ranging from 1 to 2 μm, which are called oil-bodies. An oil body has a matrix of TAG, which is surrounded by phospholipids (PL) and alkaline proteins, termed oleosins. Oleosins are highly lipophilic proteins, are expressed at high levels in many seeds and are specifically targeted to oil-bodies. Oil-bodies are abundant in plant seeds and are among the simplest organelles present in eukaryotes. They are remarkably stable both inside the cells and in isolated preparations.
Oil bodies are also termed in the literature as “oleosomes”, “lipid bodies” and “spherosomes”.